Method of copying negative photographic images by transfer of silver salt to a receiving layer



April 5, 1955 E, H LAND ETAL 2,705,676

METHOD OF' COPYING NEGATIVE PHOTOGRAPHIC IMAGES BY TRANSFER OF' SILVER SALT TO A RECEIVING LAYER Filed Aug. l, 1950 Ne aiive Ima e '2) i g g (un ((Ilp Posiiive Transfer Image ,L MNHN I4 (|4p STEP 3 bog/0030030 ofgoogoo jo@ 0/0 0,0 Q0 ,f f ,f v /Bleached Negal've Elemeni 'l un LHp Negaive Image Receiving Sheer T IO ,0,0 do Q op loro o@ g/Bleached Negaiive Elemeni 4 gg/ggglwgyqgi/{ fLquid Processing Composiiion STEP. 5

Maz/@ 4 60 INVENTORS BYEMAC ATTORNEYS United States Patent O METHOD OF COPYING NEGATIVE PHOTO- GRAPHIC IMAGES BY TRANSFER OF SIL- VER SALT TO A RECEIVING LAYER Edwin H. Land, Cambridge, and Howard G. Rogers,

Weston, Mass., assignors to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Application August 1, 1950, Serial N o. 176,962

7 Claims. (Cl. 95-88) This invention relates to photography, and more particularly to a process for copying a negative silver image, especially a negative silver image of the character obtained when carrying out a one-step photographic transfer process wherein a positive image is formed from a negative latent image.

A developed negative image of a character which is generally unsuited for the production of positive images therefrom is obtained in carrying out a one-step photographic process wherein a latent negative image in a silver halide emulsion is developed to silver with a liquid processing composition containing a photographic developer and a silver halide solvent which is permeated into the emulsion layer, and wherein unexposed silver halide in the form of silver complex is transferred from the emulsion layer to an image-receiving layer and is there developed to form a positive or reversed image of the latent negative image in the silver halide emulsion.

Objects of the present invention are to provide a method for forming a good quality copy of a negative produced in carrying out a transfer process of the character described, particularly a copy negative from which high quality positives are easily produced by the usual optical printing methods.

Other objects of the invention reside in the provision of a process for copying a negative silver image contained in a portion of a silver halide emulsion layer wherein the negative image extends from the surface at one side of the layer depthwise for at least a part of the thickness of the layer, and wherein that portion of the emulsion layer, complementary to the negative image and for at least a distance depthwise from the image side of the layer, is substantially free of light-sensitive silver salts; to provide a process of this character wherein a highly intensified copy of a negative silver image which is contained in a developed emulsion layer is formed in an image-receiving sheet material by transfer practices; and to provide a process for treating an emulsion layer containing a negative silver image by bleaching the silver of the image to a silver salt, and by transferring at least portions of said silver salt to an image-receiving sheet material and there developing the transferred portions to form a copy of the negative silver image originally contained in the emulsion layer.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

Fig. l diagrammatically illustrates, in Steps 1 and 2 thereof, procedure involved in carrying out a photographic transfer process for providing, in an image-receiving layer, a positive image of a latent negative image formed in a silver halide emulsion layer, while Steps 3, 4 and 5 illustrate procedure for processing the negative illustrated in Step 2 to provide a copy of said negative; and

Fig. 2 is a diagrammatic illustration of one embodiment of an image-receiving sheet material employed in the invention.

,7. the emulsion layer.

'ice

As it is well known to the art, a silver halide emulsion layer containing a latent image may be processed by transfer practices to form a reversed image of said latent image in a layer of image-receptive material. In carrying out a transfer process of this character, a silver halide emulsion layer is exposed, as for example in a camera. The exposed silver halide emulsion layer is then permeated with a liquid processing composition comprising a photographic developer and a silver halide solvent. Liquid composition permeated into said photosensitive emulsion develops silver in the exposed portions thereof and during development forms an imagewise distribution of soluble silver complex in the unexposed parts of the emulsion.

The soluble silver complex so formed is transferred by imbibition and in solution to an image-receiving layer located in superposed relation and in such close proximity to the emulsion layer as to receive a depthwise diffusion of liquid from the emulsion layer without appreciably disturbing said irnagcwise distribution of silver complex which is deposited on or in the image-receptive material. This deposition, i. e., the silver complex in solution, is developed by developer contained in the solution to provide a reversed image in silver of the latent image in Upon formation of the reversed image, the image-receptive material and the negative, or the photosensitive element, are separated from each other.

Steps 1 and 2 of Fig. 1 diagrammatically illustrate steps in carrying out a transfer process wherein a photographic film unit is exposed in a camera to a subject and is processed in the camera in one step to provide a positive print of the negative latent image formed upon exposure of the unit.

A photographic film unit, for this purpose, comprises a photosensitive element 10 including a silver halide emulsion layer 11 on a support 12, an image-receiving element 14 having a layer of image-receptive material on which the transfer image is formed, and a rupturable container which is not shown but which is adapted to be mounted on one of said layers and in which the liquid processing composition is carried. The various layers of the unit are held together at one end by hinge means or the like (not shown) whereby to permit separation of the photosensitive layer 11 from the image-receiving element 14 for exposure of the layer 11 from the side thereof adjacent the image-receiving layer.

Processing of the unit, after exposure of the photosensitive layer, is effected by pulling the unit between a pair of pinch or pressure rolls (not shown) which brings the image-receiving layer and the photosensitive layer into superposed relation to each other, ruptures said container and spreads the liquid contents thereof in a layer 15 between and in contact With the adjacent surfaces of the image-receiving element 14 and the photosensitive layer 11. A film unit of this character may be conveniently processed in a hand camera, as for example the camera forming the subject matter of Patent No. 2,455,111, issued November 30, 1948, to Joseph F. Carbone and Murry N. Fairbank for Photographic Apparatus for Processing a Photosensitive Film.

Step 1 of Fig. l schematically illustrates the negative photosensitive element 10 after exposure to a subject and following spreading of the liquid processing composition between and in contact with the layer 11 and the superposed image-receiving layer 14 but prior to permeation of the liquid into the layers of the unit. A latent negative image is shown in the photosensitive layer 11 of Fig. 1 as having a fully exposed portion. at the left side thereof and a completely unexposed portion at the right side thereof. Circles with a cross therein are employed to represent exposed grains of silver halide, while unexposed grains of silver halide are represented by circles without marking therein. To this convention, which is followed throughout the drawings, a showing for developed silver grains is added which employs solid dots.

In Step 1, and in fact throughout the drawing, the various layers of photographic material have been greatly exaggerated in thickness for the purpose of illustration. Similarly, the showing of the silver halide grains and of silver developed therefrom have been greatly exaggerated as to size and shape. These various grains, for the purpose of simplification and to facilitate understanding of the invention, are shown as arranged in symmetrically positioned rows which extend depthwise of the photosensitive and image-receiving layers illustrated in the drawings. It will, however, be understood to the art that this simplification recognizes that silver halide and silver derived therefrom will appear in grains many times smaller than those illustrated, that these grains will not be symmetrical in shape nor will they be symmetrically arranged either in a horizontal plane or a vertical plane.

Step 2 shows the photographic unit of Fig. l following the processing thereof by the liquid composition and With the image-receiving layer 14 and the photosensitive layer 11 separated from each other. Negative silver 11n is shown as developed in the latent image portion of the photosensitive layer 11 while grains of unexposed silver halide have been shown as removed from the unexposed portion 11p ofthe photosensitive layer 11. These removed light-sensitive silver halide grains are in effect positive-image-forming silver salts and are deposited, in the form of soluble silver complex, on an area of the image-receiving layer 14 which is complementary to the area in the emulsion 11 occupied by the developed negative silver 11n. These salts are reduced to silver 14p to provide a positive image of the latent negative image in the photosensitive element 10.

The negative image is shown in Step 2 of Fig. 1 as extending depthwise from the exposed surface of layer 11, which is also the surface into which the processing composition is permeated and for the purpose of discussion may be considered as the image side or image surface of the negative element and the photosensitive layer 11.

It is again pointed out that only some of the silver salts available for transfer for positive image formation are shown as transferred from the portion 11p of layer 11. In this regard it is believed that the removal of unexposed silver halide in the form of a silver complex is a surface phenomenon and even in a completely unexposed portion of the photosensitive layer silver halide will be removed from a stratum thereof which extends depthwise for only a minute distance from the image side of the layer, or only a part of the thickness of the emulsion. In any event, as will subsequently become apparent, the copy process of this invention is dependent upon the removal of the positive-image-forming silver salts from the negative photosensitive layer throughout a depth which represents only a part of the thickness of the photosensitive layer.

The negative in Step 2 of Fig. l is the negative produced by carrying out the transfer process and is illustrated in an unfogged condition. However, the negative 10 soon becomes dark all over. This is because the negative element and the image-receiving layer 14 are stripped apart in the light and because nearly all of the fogged silver salts remaining in the photosensitive layer 11 are reduced by excess developer which is used in processing and which itself remains in the negative layer. As a result, the negative has low contrast and often some partial reversal.

It is possible to form a positive image by optically printing the negative 10 onto suitable paper. However, it will be apparent that negative 10 will give a poor quality print. The contrast in a negative such as that shown in Step 2 of Fig. l is low, being about one-fifth to onesixth of the contrast desired for obtaining good quality .positive images by optical printing practices. The low contrast in the negative image is attributable to a number of factors. Silver grains, in a negative image formed by a transfer process, are relatively large in size and have low covering power whereas the silver which forms the positive image is finely divided and the grains thereof have a covering power which is five or six times greater than the negative grains. This means that the formation by transfer of a full density positive print requires only a small amount of light-sensitive silver halide. Under these conditions, by far the greater quantity of positiveimage-forming silver salts available for transfer will remain in the photosensitive layer. However, light-sensitive silver salts which remain in the negative element, and which become fogged, reduce the contrast of the negative still further, depending upon the amount by which they become fogged.

Inherently, however, the negative element 10, processed by a one-step photographic method, has a high quality negative image present adjacent that surface thereof which was subjected to development. It therefore becomes desirable to extract this high quality negative image from the negative element while leaving deposits therein which detract from the contrast of the negative and its continuity of tone reproduction. These practices involve bleaching the negative silver to a substantially insoluble and light-sensitive or insensitive silver salt which is substantially nonspontaneously developable, at least by a liquid processing composition similar in character to that previously mentioned as comprising a photographic developer and a silver salt solvent. Such a composition, as will more fully appear, is adapted to be permeated into the negative element after the negative silver has been bleached to a silver salt for the purpose of transferring a portion of the silver salt formed by bleaching from the layer 11 to an image-receiving sheet.

A conventional silver bleach, of which there are many well known examples for photographic use, is employed for bleaching the negative element. For illustrative. purposes potassium ferricyanide is named as a preferred bleaching agent and is adapted to be employed in aqueous solution. If silver is to be bleached to silver halide, an appropriate halogen salt and potassium ferricyanide are employed in the bleach. It is to be understood, however, that practice of the invention is not restricted to the use of a silver bleach comprising potassium ferricyanide but may be carried out with any of the well known photographic bleaches which are capable of converting silver to a silver salt of the above noted characteristics.

A preferred negative emulsion for the photosensitive layer 11 is a relatively fast orthochromatic gelatino iodobromide emulsion of the Verichrome type made by Eastman Kodak Company. A bleach for converting 'developed silver in an emulsion of this character to lightsensitive silver halide comprises an aqueous solution of potassium ferricyanide and potassium bromide. When a silver chloride emulsion is employed, potassium chloride is preferred for the halogen constituent of the bleach if silver is to be converted to silver halide, although it is possible to employ potassium bromide in these circumstances. The negative silver will be bleached to relatively insensitive silver ferrocyanide in instances wherein a bleach is employed which comprises potassium ferricyanide without the addition of the halogen salt thereto.

Before bleaching, the negative element 10 is preferably washed in water for the purpose of removing excess developer and silver halide solvent which may remain in the emulsion after transfer processing. Upon completion of bleaching, the negative element 10 is again preferably washed to remove silver bleach therefrom. Following washing, bleaching and rewashing, the photosensitive element takes on an appearance similar to that indicated in Step 3 of Fig. l wherein the portion 11n contains grains of insoluble silver salt, while the portion 11p from which positive-image-forming silver salts were removed by transfer remains substantially unchanged from its condition in Step 2.

Further procedure for copying the negative image resides in permeating a liquid processing composition comprising a photographic developer and a silver salt solvent into the bleached and washed negative element 10 and effecting a transfer of light-sensitive silver salts from the rehalogenated portion 11n thereof to a permeable image-receiving sheet material 40 arranged in superposed relation and relatively close proximity thereto. This liquid composition, as previously pointed out, is substantially similar to the liquid composition used in carrying out the transfer process from which the developed negative of Step 2 of Fig. 1 was derived. Introduction of the liquid processing composition into the negative element 10 must be from the image side thereof, i. e., the surface thereof from which the negative image extends and from which silver halide was removed while processing to form the positive image.

A liquid processing composition may be introduced into the bleached and washed negative element 10 in a number of ways. For example, a permeable, image-receiving sheet 40, such as that shown in Step 4 of Fig. l, may be immersed into the liquid composition or the liquid composition may be coated onto a surface of sheet material 40, following which the sheet material is brought into superposed relation with the negative element 10 and in position to transfer the liquid composition into the negative element. In lieu of this practice, the image side of the washed and bleached negative element may be coated with a liquid composition and the image-receiving sheet brought into transfer relationship therewith.

Alternatively, the image-receiving sheet material 60 of Fig. 2 may be employed. Sheet material 60 comprises a support for an image-receiving layer on which a rupturable liquid container 61 is mounted. The liquid composition is included within the container which is ruptured upon bringing the structure 60 into superposed relation with the bleached negative element 10 and passing the combined unit between pressure or pinch rolls whereby to rupture the container and spread its liquid contents between the adjacent surfaces of the image-receiving sheet material 60 and the negative element.

Whatever method is used for permeating liquid composition into the bleached negative element 10, Step 4 of Fig. 1 illustrates the negative element and image-receiving sheet material in superposed relation with a layer of liquid processing composition shown between and in contact with the adjacent surfaces of the negative element and the sheet material and before the liquid has permeated into layer 11.

As a result of introducing the liquid processing composition into the bleached negative element 10, negativeimage-forming silver salts are transferred in solution in the liquid composition from the negative portion 11n to a corresponding portion in the image-receiving sheet material 40. The transferred silver salts are in the form of a silver complex which is developed in the image-receiving sheet material 40 to negative silver by developer contained in the processing composition.

The result of development is shown in Step 5 of Fig. l wherein a negative image which is a copy of the negative image of Step 2 is formed in the layer 40. It will be recalled that in the formation of the positive transfer image, silver halide was removed from the portion of the negative element 10 which is complementary to the developed negative image therein. Consequently, silver salts contained in the element 10, following bleaching, will be located closely adjacent the surface of the element 10 only over the negative portion thereof and it appears to be only these silver salts adjacent the surface of the element 10 which engage in the formation of the negative copy image. Suffice it to say that copy negatives of good quality have been obtained by the practices heretofore set forth.

All processing, beginning with bleaching of the negative element 10, is preferably carried out in the absence of actinic light until formation of the transfer negative image has been completed. Imbibition time for forming the negative transfer oi' copy image, i. e., the time the negative element 10 and the image-receiving sheet material 40 are maintained in contact, is for about one minute, after which the image-receiving sheet material and the negative element 10 are separated from each otheras by stripping. Partial separation of the image-receiving sheet material 40 from the negative element 10 is shown in Step 5 of Fig. 1.

As heretofore intimated, the emulsion of the negative element 10 may comprise any conventional silver halide emulsion. A preferred emulsion for this purpose is a relatively fast orthochromatic silver halide emulsion such as that previously mentioned.

The image-receiving sheet material, upon which the copy of the original negative is made, may be a substantially transparent material or one which is .more difiicultly penetrable by printing light. In the latter instance, baryta paper may be named as an example. Preferably, however, the image-receiving sheet material is transparent, as in a conventional negative, and a preferred example thereof is provided by coating gelatin on a transparent film base such as cellulose acetate. However. other transparent materials may be employed either by themselves or supported upon a transparent base. Examples of other transparent materials comprise regenerated cellulose, a polyhydroxyalkane, such as polyvinyl alcohol, sodium alginate, cellulose ethers, such as ethyl cellulose or their derivatives, such as sodium carboxymethyl cellulose, aluminum carboxymethyl cellulose, hydroxyethyl cellulose, glue, albumen, and the like.

Improvements in the photographic characteristics of a positive image obtained by transfer may be achieved by suitably treating the surface of the positive imagereceiving layer before use thereof by applying to said surface suitable substances for attracting and aggregating the image-forming ions of the transferred silver complex. These improvements relate to the color of the image and increase in contrast by increasing the density in the dark areas. A similar improvement in the photographic characteristics in the copy negative may be obtained by treatment of the surface of the image-receiving sheet material 40 or 60 in a similar manner. Examples of such substances are the metallic sulfides, such, for example, as lead sulfide, cadmium sulfide, zinc sulfide, ferric sulfide, antimony sulfide, manganous sulfide, titanium sulfide, sodium sulfide, lanthanum sulfide, palladium sulfide, nickelous sulfide, and such metallic selenides as zinc selenide, nickel selenide, lead selenide, manganous selenide and antimony selenide, and such other substances as dithiooxamide and its lead and zinc complexes, potassium dithiooxalate and the lead complexes thereof, and thioacetamide.

These precipitating materials are preferably applied to the surface of the image-receiving sheet material 40 or 60 in which the negative copy image is to be formed in mixtures of a suitable, relatively inert material such as silica aerogel (Santocel C), wood flour, clays, for example kieselguhr and bentonite, starches, ground glass, and celites.

As a specific example of incorporating precipitating components in the sheet material for the negative copy image, either of the materials 40 or 60 is run through a bath which is kept in contact with the image-receiving surface of the sheet for approximately l0 seconds, the bath comprising:

Cadmium acetate g..- 9 Neutral lead acetate g-- .3 Zinc nitrate g-- 18 Water ce The sheet thus obtained is dried and over-coated with a mixture comprising:

Water cc 270 Cadmium acetate g..- 27.8 Lead acetate g-- 9.3 Zinc nitrate g 55.6 Silica aerogel (Santocel C) g-- 3() 3% solution of sodium sulfide cc 94.7

The sheet is preferably dipped into this mixture and the excess mixture is removed from the sheet as, for example, by the action of a soft buffer roll on said sheet as it leaves the bath.

While the use of precipitating materials has been indicated as being preferred, it is to be understood that transfer images may be obtained without the employment thereof.

As previously mentioned, one bleach for converting silver to light-sensitive silver halide comprises an aqueous solution of potassium ferricyanide and a halogen salt. An example thereof, suitable for use with an orthochromatic emulsion of the character described, is as follows:

Potassium ferricyanide grams-- l5 Potassium bromide do 7.5 Water cc 500 Another example of a bleach comprises a mixture of equal parts of a 21/2% aqueous potassium ferricyanide and 212% aqueous sodium bromide solutions. The negative element 10 is bleached by immersion in either of the just noted baths for about one minute.

In general, a relatively weak aqueous solution of potassium ferricyanide may be used in instances where the negative silver is to be converted to silver ferrocyanide. However, and as it will be understood by the art, the potassium ferricyanide should be in a sufficiently concentrated solution so as to effect a reasonably complete bleaching of the silver to silver ferrocyanide within a reasonable time limit. To speed up the reaction leading to the formation of silver ferrocyanide, it is desirable to have the potassium ferricyanidesolution in a slightly acid or alkaline condition. A small quantity of sodium hydroxide added to the solution is recognized as an effective accelerator. The bleaching time, as intimated, will depend upon the concentration of the bleach and the use of an accelerator. It may be here pointed out that silver ferrocyanide is soluble in a silver halide solvent, such as the sodium thiosulfate disclosed in examples of liquid processing compositions appearing herein, and

when so dissolved forms a silver complex which is transferrable, in solution, to an image-receiving sheet where the silver of the transferred complex is developed by developer contained in the processing composition. An advantage in the use of potassium ferricyanide by itself resides in the fact that it bleaches silver to a relatively insensitive silver salt, namely, silver ferrocyanide. This permits the bleached negative to be handled without that care required to prevent exposure which is necessary in the handling of a more sensitive silver salt, such as silver halide.

As one example of a liquid processing composition, the following formulation is given:

Water grams 1860 Sodium sulfite do 78 Sodium hydroxide do 74.6 Sodium thiosulfate do 14.5 Citric acid do 38.5 Hydroquinone do 52 The liquid processing composition, just set forth, is particularly adapted for use by immersing the negative image-receiving sheet material 40 or 60 in the composition and then bringing the sheet material into contact with the negative element 10. However, if the viscosity of this composition is suitably increased, it is' particularly useful for application from a rupturable container as in the structure of Fig. 6. For this purpose a lmforming material is included in the composition in suitable quantities to impart thereto a viscosity in excess of 1000 centipoises at a temperature approximating 24 C. and preferably of the order of 1000 to 200,000 centipoises at saidV temperature. The desired viscosity may be obtained by including 117 grams of sodium carboxymethyl cellulose in the formula just given for the processing composition.

Another example of a suitable liquid processing composition of low viscosity comprises an aqueous solution of a hydroquinone caustic developer and sodium thiosulfate in the following proportions:

Hydroquinone caustic developer cc 100 50% sodium thiosulfate solution cc 2O Water cc 50 A suitable hydroquinone caustic developer comprises:

Water liters 3 Sodium sulte, des grams 360 Hydroquinone do..-" 180 Sodium hydroxide do 150 Potassium bromide do 120 Water to make liters-- 4 The secondly described liquid processing composition is used in carrying out practices of this invention in a manner similar to that set forth in connection with the first described composition. If desired, a viscosity increasing compound, such as sodium carboxymethyl cellulose, may be added to the secondly described liquid processing composition.

In the usual practice of a transfer process, the negative derived therefrom is discarded or destroyed as being substantially valueless, especially for reproduction purposes. The significance of the present invention resides in the ability to obtain a permanent copy of this negative whereby copies of the original print may be made at will without the necessity of employing the positive print for reproduction purposes.

As it will be appreciated, a good quality copy of a relatively poor negative, i. e., a negative veiled with fog and of low intensity, may be obtained by the practices of this invention. Copy negatives formed by the methods herein set forth are of a stable character and are usable indefinitely in the manner of conventional negatives for producing positive prints by well known optical printing procedures.

While primarily concerned with obtaining a copy of a negative produced in carrying out a transfer process, the present invention gains added significance in its ability to copy developed and xed out photographic originals which have been prepared by classical wet processing and it will be understood that the scope of the invention includes the practice thereof for this purpose. The usefulness of the invention in this regard may be illustrated, for example, by the preparation from a developed and fixed out negative or positive of a framed print wherein a selected part of the scene of the original is copied or reproduced by practices which involve the application over the area of the original to be copied of the silver bleach heretofore mentioned, followed by the transfer processing previously set forth.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. ln a transfer process wherein a photosensitive emulsion layer containing silver halide of substantially uniform light-sensitive characteristics has latent image silver halide formed therein to extend from one side of said emulsion layer depthwise of said layer and an alkaline liquid reagent comprising a silver halide developer and a silver halide solvent is permeated into the emulsion layer to develop the latent image contained therein to a silver image and to form with the unexposed silver halide a silver complex, and wherein the silver complex in solution in said reagent is transferred by imbibition from substantially only a surface stratum, located adjacent said side of said emulsion layer, to an image-receiving layer which is permeable to said liquid reagent and which is held in superposed relation to said emulsion layer adjacent said side of said emulsion layer to leave behind, in a portion of the emulsion layer, complementary to said silver image, a stratum of substantially unexposed silver halide and, in superposed relation to said stratum of unexposed silver halide, said surface stratum from which said silver complex has been transferred, and wherein the silver of said transferred complex is developed by said developer in said image-receiving layer to form in said imagereceiving layer a reverse image of said latent image and said emulsion layer and image-receiving layer are separated from said superposed relation following the transfer of said complex to said image-receiving layer, a method of providing a copy of the silver image remaining in said silver halide emulsion layer following the transfer of said silver complex therefrom to provide said reverse image, which comprises permeating into said emulsion layer, without xing out unexposed silver halide remaining therein after the formation of said reverse image, a silver bleaching agent and by means of said bleaching agent converting the developed silver in the emulsion layer to a substantially water-insoluble silver salt, without forming a developable latent image in said water-insoluble silver salt spreading an alkaline liquid composition between and in contact with said side of said emulsion layer and an image-receiving sheet material which is permeable to said liquid composition and which is arranged in superposed relation to said emulsion layer adjacent said side of the emulsion layer, said liquid composition comprising a mixture of a silver halide developer and a substance capable of forming with said water-insoluble silver salt a soluble silver complex which is reducible to silver by the developer in said composition, permeating said composition into said emulsion layer and dissolving, by means of said composition permeated into the emulsion layer, substantially only the waterinsoluble silver salt derived from bleaching said silver image, said composition comprising said mixture of developer and said solvent having a negligible reducing action on said water-insoluble silver salt during the formation of said silver complex by dissolution in said composition and, without developing said dissolved silver complex in solution in said composition in said emulsion layer, transferring said complex in solution in said cornposition and by imbibition to said image-receiving sheet material and there reducing said transferred complex to silver with said developer to provide in the image-receiving sheet material a silver image which is a copy of said original silver image, and thereafter separating said emulsion layer and said image-receiving sheet material from said superposed relation.

2. A process for providing a copy of a silver image derived by photoexposing and developing a photosensitive silver halide layer which contains silver halide of sub stantially uniform sensitivity and which, following exposure and development, is provided in a portion thereof with a silver image which extends from the surface at one side of said layer depthwise for at least a part of the thickness of the layer, and wherein that portion of said layer, complementary to said silver image, contains a stratum of substantially unexposed silver halide and, 1n superposed relation to said stratum of unexposed silver halide, a stratum which is substantially free of lightsensitive silver salt and which extends from the image side of said layer at least for a distance depthwise of said layer, the steps comprising applying substantially exclusively to said image side of said photosensitive layer suflcient silver bleaching agent to bleach the silver of said image in at least a portion of said image which extends depthwise from said image side of said layer and converting the silver in said portion to a substantially water-insoluble silver salt, Without forming a developable latent image in said water-insoluble silver salt applying substantially exclusively to said image side of said emulsion layer and absorbing into said emulsion layer a liquid composition which comprises a mixture of a silver halide developer and a substance Vcapable of forming with said water-insoluble silver salt a soluble silver complex which is reducible to silver by the developer in said mixture, dissolving, by means of said composition absorbed into said emulsion layer, the Water-insoluble silver salt present in a stratum of the bleached portion extending from said side depthwise of said emulsion layer for a thickness at least restricted to the minimum thickness possessed by said stratum of said photosensitive layer which is free of said light-sensitive silver salt, said composition comprising said developer and said solvent having a negligible reducing action on said water-insoluble silver salt during the formation of said silver complex by dissolution in said composition and without developing dissolved silver complex in solution in said composition in said photosensitive layer and while the photosensitive layer is wet with said composition bringing said photosensitive layer and an image-receiving sheet material which is permeable to said composition into superposed and adjacent relation to each other with said image side of said photosensitive layer next to said sheet material and transferring said complex in solution in said composition and by imbibition to said image-receiving sheet material and there reducing said transferred complex to silver with said developer to provide in the imagereceiving sheet a silver image which is a copy of said original silver image, and thereafter separating said photosensitive layer and said image-receiving sheet material from said superposed relation.

3. A process of the character defined in claim 1 including the steps of washing the silver halide emulsion layer before bleaching the silver image therein and also been converted to said water-insoluble silver salt and,

before said liquid composition is permeated into said emulsion layer.

4. A process of the character defined in claim 1 wherein said image-receiving sheet material is substantially transparent.

5. A process of the character defined in claim 1 wherein a rupturable container, having said alkaline liquid composition therein, is positioned between said emulsion layer and said image-receiving sheet material adjacent one edge thereof and wherein said process includes the step of applying pressure to the outer surfaces of said emulsion layer and said image-receiving sheet material to rupture said container and bring said emulsion layer and image-receiving sheet material into superposed relation with each other While spreading the liquid contents of said container between and in contact with the adjacent surfaces of the superposed emulsion layer and the image-receiving sheet material.

6. A process of the character dened in claim 2 wherein said image-receiving sheet material is substantially transparent.

7. A process of the character dened in claim 2 including the step of Washing said photosensitive layer after converting the silver image therein to said waterinsoluble silver salt.

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Varden, PSA JOURNAL, vol. 13, September 1947, pp. 551-554.

Land, Journ. Opt. Soc. Am., vol. 37, No. 2, February 1947, PP. 61-77. 

1. IN A TRANSFER PROCESS WHEREIN A PHOTOSENSITIVE EMULSION LAYER CONTAINING SILVER HALIDE OF SUBSTANTIALLY UNIFORM LIGHT-SENSITIVE CHARACTERISTICS HAS LATENT IMAGE SILVER HALIDE FORMED THEREIN TO EXTEND FROM ONE SIDE OF SAID EMULSION LAYER DEPTHWISE OF SAID LAYER AND AN ALKALINE LIQUID REAGENT COMPRISING A SILVER HALIDE DEVELOPER AND A SILVER HALIDE SOLVENT IS PERMEATED INTO THE EMULSION LAYER TO DEVELOP THE LATENT IMAGE CONTAINED THEREIN TO A SILVER IMAGE AND TO FORM WITH THE UNEXPOSED SILVER HALIDE A SILVER COMPLEX, AND WHEREIN THE SILVER COMPLEX IN SOLUTION IN SAID REAGENT IS TRANSFERRED BY IMBIBITION FROM SUBSTANTIALLY ONLY A SURFACE STRATUM, LOCATED ADJACENT SAID SIDE OF SAID EMULSION LAYER, TO AN IMAGE-RECEIVING LAYER WHICH IS PERMEABLE TO SAID LIQUID REAGENT AND WHICH IS HELD IN SUPERPOSED RELATION TO SAID EMULSION LAYER ADJACENT SAID SIDE OF SAID EMULSION LAYER TO LEAVE BEHIND IN A PORTION OF THE EMULSION LAYER, COMPLEMENTARY TO SAID SILVER IMAGE, A STRATUM OF SUBSTANTIALLY UNEXPOSED SILVER HALIDE AND, IN SUPEROSED RELATION TO AND STRATUM OF UNEXPOSED SILVER HALIDE, SAID SURFACE STRATUM FROM WHICH SAID SILVER COMPLEX HAS BEEN TRANSFERRED, AND WHEREIN THE SILVER OF SAID TRANSFERRED COMPLEX IS DEVELOPED BY SAID DEVELOPER IN SAID IMAGE-RECEIVING LAYER TO FORM IN SAID IMAGE-RECEIVING LAYER A REVERSE IMAGE OF SAID LATENT IMAGE AND SAID EMULSION LAYER AND IMAGE-RECEIVING LAYER ARE SEPARATED FROM SAID SUPERPOSED RELATION FOLLOWING THE TRANSFER OF SAID COMPLEX TO SAID IMAGE-RECEIVING LAYER, A METHOD OF PROVIDING A COPY OF THE SILVER IMAGE REMAINING IN SAID SILVER HALIDE EMULSION LAYER FOLLOWING THE TRANSFER OF SAID SILVER COMPLEX THEREFROM TO PROVIDE SAID REVERSE IMAGE, WHICH COMPRISES PERMEATING INTO SAID EMULSION LAYER TO A SUBSTANTIALLY WATER-INSOLUBLE SILVER REMAINING THEREIN AFTER THE FORMATION OF SAID REVERSE IMAGE, A SILVER BLEACHING AGENT AND BY MEANS OF SAID BLEACHING AGENT CONVERTING THE DEVELOPED SILVER IN THE EMULSION LAYER TO A SUBSTANTIALLY WATER-INSOLUBLE SILVER SALT, WITHOUT FORMING A DEVELOPABLE LATENT IMAGE IN SAID WATER-INSOLUBLE SILVER SALT SPREADING AN ALKALINE LIQUID COMPOSITION BETWEEN AND IN CONTACT WITH SAID SIDE OF SAID EMULSION LAYER AND AN IMAGE-RECEIVING SHEET MATERIAL WHICH IS PERMEABLE TO SAID LIQUID COMPOSITION AND WHICH IS ARRANGED IN SUPERPOSED RELATION TO SAID EMULSION LAYER ADJACENT SAID SIDE OF THE EMULSION LAYER, SAID LIQUID COMPOSITION COMPRISING A MIXTURE OF A SILVER HALIDE DEVELOPER AND A SUBSTANCE CAPABLE OF FORMING WITH SAID WATER-NSOLUBLE SILVER SALT A SOLUBLE SILVER COMPLEX WHICH IS REDUCIBLE TO SILVER BY THE DEVELOPER IN SAID COMPOSITION PERMEATING SAID COMPOSITION INTO SAID EMULSION LAYER AND DISSOLVING, BY MEANS OF SAID COMPOSITION PERMEATED INTO THE EMULSION LAYER, SUBSTANTIALLY ONLY THE WATERINSOLUBLE SILVER SALT DERIVED FROM BLEACHING SAID SILVER IMAGE, SAID COMPOSITION COMPRISING SAID MIXTURE OF DEVELOPER AND SAID SOLVENT HAVING A NEGLIGIBLE REDUCING ACTION ON SAID WATER-INSOLUBLE SILVER SALT DURING THE FORMATION OF SAID SILVER COMPLEX BY DISSOLUTION IN SAID COMPOSITION AND, WITHOUT DEVELOPING SAID DISSOLVED SILVER COMPLEX IN SOLUTION IN SAID COMPOSITION IN SAID EMULSION LAYER, TRANSFERRING SAID COMPLEX IN SOLUTION IN SAID COMPOSITION AND BY IMBIBITION TO SAID IMAGE-RECEIVING SHEET MATERIAL AND THERE REDUCING SAID TRANSFERRED COMPLEX TO SILVER WITH SAID DEVELOPER TO PROVIDE IN THE IMAGE-RE CEIVING SHEET MATERIAL A SILVER IMAGE WHICH IS A COPY OF SAID ORIGINAL SILVER IMAGE, AND THEREAFTER SEPARATING SAID EMULSION LAYER AND SAID IMAGE-RECEIVING SHEET MATERIAL FROM SAID SUPERPOSED RELATION. 